Because of their unique sieving characteristics as well as their catalytic properties, crystalline molecular sieves and zeolites are especially useful in applications such as hydrocarbon conversion, gas drying and separation.
Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework type zeolites and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three-letter code and are described in the “Atlas of Zeolite Framework Types,” Sixth Revised Edition, Elsevier (2007).
One known molecular sieve for which a structure has been established is the material designated as AFX, which is a molecular sieve having pores defined by intersecting channels formed by 8-membered rings of tetrahedrally coordinated atoms and which have cross-sectional dimensions of about 3.4 Å by about 3.6 Å. Examples of AFX framework type molecular sieves include SAPO-56 and SSZ-16. AFX framework type molecular sieves can be potentially useful in sorptive separations, for example of methane from carbon dioxide, and in catalyzing chemical reactions, including the conversion of oxygenates to olefins (OTO) and the selective reduction of NOx in combustion exhaust gases, where small pore size is desirable.
U.S. Pat. No. 4,508,837 discloses zeolite SSZ-16 and its synthesis in the presence of an organic nitrogen-containing species derived from 1,4-di(1-azoniabicyclo[2.2.2]octane) lower alkane compounds.
U.S. Pat. No. 5,194,235 discloses the synthesis of zeolite SSZ-16 from a reaction mixture containing DABCO-Cn-diquat cations, where DABCO represents 1,4-diazabicyclo[2.2.2]octane and n is 3, 4, or 5.
U.S. Pat. No. 5,370,851 discloses the synthesis of molecular sieve SAPO-56 from a reaction mixture containing N,N,N′N′-tetramethylhexane-1,6-diamine.
U.S. Pat. No. 8,562,942 disclose the synthesis of an aluminosilicate AFX framework type zeolite using 1,3-bis(1-adamantyl)imidazolium cations as a structure directing agent.
According to the present disclosure, it has now been found that hexamethonium dications, 1,6-bis(N-methylpyrrolidinium)hexane dications, and 1,4-bis(N-methylpyrrolidinium)butane dications can be effective as structure directing agents in the synthesis of AFX framework type molecular sieves.